Thoracic Surgery II Flashcards
Formula for O2 content
(Hgb)(O2 Sat)(1.39) + (PaO2)(.003)
Physiologic responses to hypoxia
Increased CO
HTN
Increased ventilation
Sats 60-80% = tachycardia and hypotension
Sats < 60% = bradycardia and hypotension
Kids have this pronounced response to hypoxia
Bradycardia
Predictors of hypoxia on single lung ventilation
Poor PaO2 on two lung ventilation High perfusion to lung being removed Right thoracotomy Problems with desaturation in the supine position Restrictive diseases
This is the biggest predictor of hypoxia on single lung ventilation
Poor PaO2 on two lung ventilation
Saturation values and their correlated PaO2
90% = 70mmHg 80% = 50 60% = 35 20% = 15
These factos cause a leftward shift of the dissociation curve
Alkalosis
Cold
Decreased 2,3-DPG
These factors cause a rightward shift of the dissociation curve
Acidosis
Hyperthermia
Increased 3,4-DPG
What is the difference between hypoxia and hypoxemia?
Hypoxia is low O2 tension at the cellular level and reflects tissue hypoxia.
Hypoxemia is the relative lack of enough O2 in arterial blood.
Hypoxemia is defined as a PaO2 < _____mmHg
80mmHg
Common causes of hypoxia
- Low FiO2
- Hypoventilation
- V:Q mismatch from compression d/t atelectasis or pulmonary edema
- Decreased O2 carrying capacity (anemia, bleeding, etc)
- Leftward shift of the dissociation curve (alkalosis, hypothermia, decreased 2,3-DPG, hypocarbia)
Possible reasons for hypoxia during anesthesia
Mechanical failure***** --> most common cause - Disconnect of circuit from the ETT (most common) - Empty cylinders - Pipeline failure Esophageal intubation Hypo or hyperventilation Decreased FRC Right to left shunt PE ARDS
Clinically effective range of O2 therapy
.24-.5 FiO2
Detrimental effects of O2 therapy
Hypoventilation (especially in those with COPD)
O2 Toxicity
- Avoid 100% O2 for > 12 hours
- Avoid 80% O2 for > 24 hours
- Avoid 60% > 36 hours
Retrolental fibroplasia (common in newborns on high FiO2)
Fire hazard
Absorption atelectasis (gas rapidly diffuses into the blood and alveolar collapse occurs)
Clinical goal for O2 therapy
Sat > 90%
Which correlates to a PaO2 of 60-70mmHg
S/S of O2 toxicity
Substernal pain Mild carinal irritation Cough Impairment of ciliary motion Alveolar epithelial damage Interstitial fibrosis
A face mask can deliver up to this FiO2
Up to 60%
A facemark with a reservoir can deliver these FiO2s
6L/min = 60% 7 = 70% 8 = 80% 9 = > 80% (around 90%) 10 = >80% (around 100%)
This is the gold standard to prevent respiratory depression in thoracic cases
Thoracic epidural
What is the most common reason for not maintaining respiration after surgery?
Impaired respiratory drive.
This is why we prefer thoracic epidural to opioids!
Tidal volumes during jet ventilation
Provides tidal volumes less than anatomical deadspace
Two most common post-op complications
Atelectasis and pneumonia
When should ABGs be obtained?
On room air, on double lung ventilation, 15 minutes after one lung ventilation, and every hour or as clinical condition requires
Tiers of Intra-op Monitoring for Thoracic Surgery
Tier I
- Otherwise, routine, healthy patients like young person getting a VATS
- Need a-line
Tier II
- Healthy patient undergoing a specialized procedure, or, a sick patient undergoing a routine procedure
- Significant cardiopulmonary disease or mild lung disease patient undergoing one lung ventilation (OLV)
- Significant interstitial lung disease who requires an open lung biopsy or lobectomy
- Need a-line and CVP. Possible PAC.
Tier III
- Sick patients with significant cardiopulmonary complications who will probably be getting sicker and have special intra-op needs
- Patient with cor pulmonale
- Needs a-line, CVP, and PAC
- Mixed venous monitoring
- Probably TEE
If PaO2 is > ____, then you’re probably not going to have issues with oxygenation on OLV. If < ____, then you probably will.
> 400 = ok
< 200 you make have problems
Normal TVs for OLV
5-6mL/kg
What is intrapulmonary shunt?
When part of the lung is being perfused, but not ventilated.
What stimulated hypoxic pulmonary vasoconstriction?
Alveolar hypoxia
What are silent lung units?
Areas of the lung that have had blood shunted away from them d/t hypoxic pulmonary vasoconstriction
Hypoxic pulmonary vasoconstriction and OLV
Blood ends up getting shunted away from the non-dependent lung and towards the dependent lung
What is unique about hypoxic pulmonary vasoconstriction (HPV)?
In other parts of the body, vessels dilate in response to hypoxia. This is the opposite in the lungs and works to our favor by shunting blood away from the shitty parts of our lungs and towards the parts that are working well.
HPV hits its maximal effect at ___ and lasts for up to ___.
Peaks at 30 minutes, and lasts for about 2 hours.
Mechanism of action of HPV
Exact mechanism is unclear
HOWEVER, it may be due to the direct action of alveolar hypoxia on pulmonary smooth muscles sensed by the mitochondrial electron chain, with reactive O2 species serving as a second messenger to increase calcium and cause smooth muscle constriction.
Endothelial derived molecules modulate the primary response.
Other humoral and neurogenic influences are probably involved.
Factors that inhibit HPV
High or low PA pressures Hypocapnea (d/t hyperventilation) High or low mixed venous blood Vasodilators (NTG, nipride, etc) Pulmonary infections Inhaled anesthetics
Effect of HPV on left to right shunting
HPV will improve right to left shunting. Without it, blood would be going to areas of the lung not being perfused, resulting in Deoxygenated reaching the left heart. With it, blood is not exposed to these shitty lung areas and all blood gets properly oxygenated, thus decreasing right to left shunting.
Effect of inhaled anesthetics on HPV
Most IAs inhibit HPV once greater than 1 MAC.
Below 1 MAC, you’re good.
IAs have a dose-dependent effect on HPV
How do IV agents affect HPV?
They don’t.
Effect of nitrous on HPV
Clinically insignificant
1MAC of isoflurane inhibits HPV by ____%
21%
Factors that place a patient at increased risk for desaturation on OLV
High percentage of ventilation or perfusion to the operative lung (as seen on scan)
Poor PaO2 on two lung ventilation (especially in the lateral position)
Right sided thoracotomy (because the right side is 10% larger –> means there will be a larger intrapulmonary shunt that occurs when this lung is deflated)
OLV causes this type of shunt
Right to left shunt. This occurs because the lung is still getting blood flow but is not being ventilated during the case. The degree of this shunt, however, is diminished by HPV. But remember that gases > 1MAC will reduce this response and worsen intrapulmonary shunt!
How might shunt be worsened in the VENTILATED lung during OLV?
Anything that would decrease blood flow to the ventilated lung:
- High airway pressures
- Low FiO2 (causes HPV in the lung where we don’t want it)
- Vasoconstrictors
- PEEP
Benefits of inhaled anesthetics in thoracic surgery
Good bronchodilators and obtunds airway reflexes
Can be delivered with high FiO2 concentrations
Relatively CV stable
Rapidly removed from the system if needed
HPV is preserved at levels up to 1 MAC
Benefits of IV agents in thoracic surgery
CV stability
No affect on HPV
Decreases the need for high volatile anesthetics
Nitrous in thoracic surgery
Has no clinical affect on HPV, but remember that to be effective it must be used in high concentrations. This is undesirable because we try to give high FiO2 during the case.
We want to any fluid intake over ____ in a 24 hours period
20mL/kg
ex- 1400cc for a 70kg patient
What should you include in your epidural medications?
Low concentration local plus an opioid (the other day we used fentanyl + buvipicaine). We gave bolus doses during the case and then started a maintenance drip in the ICU.
What sucks about referred shoulder pain after thoracotomy?
It can persist despite have a thoracic epidural.
What can be used to treat refractory shoulder pain?
NSAIDs (Toradol), but we need to be careful because they increase bleeding and we have an epidural in place. We don’t want no epidural hematoma. That would be bad, mmmkay?
We should reduce thoracic epidurals dosing to about __% of the dose that you would give for lumbar epidurals.
50%
This is to avoid cephalic spread.
Why do we usually avoid morphine in these cases?
They cause more respiratory depression than fentanyl. Fentanyl has less respiratory depression and is cardiac stable.
According to the powerpoint, about how much fentanyl should you give on induction?
3-6mcg/kg, but really you probably won’t give this much because you would have your thoracic epidural in place and shouldn’t need to much pain control.
How many interspaces should get blocked in an intercostal nerve block?
5 interspaces. Should be one at the site as well as two interspaces above an two below the site.
Indications for OLV
ABSOLUTE Indications:
- To isolate a lung to avoid spillage or contamination (fistula/empyema)
- To control distribution of ventilation
- Unilateral bronchopulmonary lavage for pulmonary alveolar proteinosis (excessive abnormal surfactant –> treatment is lavage of the entire lung)
RELATIVE Indications:
- To improve surgical exposure
- Severe hypoxemia d/t unilateral lung disease (do OLV to increase HPV, thus decreasing right to left shunt)
This is the lung separation technique of choice
Double lumen tube (chosen over bronchial blockers or endobronchial intubation)
This is the best predictor of DLT size
Height! Cause that shit needs to go far down your trachea.
People taller than 170cm, should receive this size DLT
41 FR
Average DLT size
37 or 39 FR
Usually for those 63-67 inches
Complications for DLTs
Tracheobronchial tree disruption
Traumatic laryngitis
Suture of pulmonary vessels to the DLT
What is a univent tube?
Single lumen (uni) tube that has a special channel for placement of a bronchial blocker
How to check placement for a left sided DLT
Inflate the tracheal cuff
Check for bilateral breath sounds (if unilateral, it means that it has gone so far down the left maintop that the tracheal opening is blocked)
Inflate the bronchial cuff and clamp the tracheal lumen and make sure you only hear left breath sounds
Then clamp the bronchial lumen only and make sure you only hear right breath sounds.
During OLV. minute ventilation should be adjusted so that PaCO2 is about ___mmHg
40mmHg
Interventions to do if you begin having trouble with oxygenation during OLV
Try suctioning the tube (might be shit in there)
Re-assess positioning with fiberoptic scope
Give PEEP to ventilated lung
Give CPAP to non-dependent lung (5-10cmH2O)
Ensure that MAC < 1 (over this could result in R to L shunt from impaired HPV)
Try recruitment maneuver with non-dependent lung (vagal maneuver with 20cmH2O for about 15-20 seconds –> we would have to discuss this with the surgeon first)
When re-inflating the down lung, you should re-inflate it to about ____cmH2O to reinstall the atelectic area and check for air leaks
30cmH2O
When checking chest tube potency, it should only be at this setting
To water seal only, no suction.
Weaning parameters
VC > 15mL/kg TV > 2mL/kg RR < 30 ABGs look decent Infection free LOC is appropriate Pain is under control
Criteria for extubation
Acute phase of the disease is resolved and adequate cough reflex is present***
Hemodynamic stability
RR is < 20-30
PaCO2 is normal
PaO2 > 60 on FiO2 of 40-50 and PEEP < 5-10
Adequate LOC (GCS > 13)
Mortality rate for mediastinoscopy can be as high as __%
8%
Can mediastinoscopy be done under LA only?
Yes, but 90% are done with single or double lumen ETT.
Major risk may be involved if local only, b/c if the patient coughs, there is major risk of bleeding and damage to the great vessels or other structures
Mediastinoscopy is the gold standard for
evaluation of mediastinal lymph nodes in the staging of NSCLC, in the diagnosis of mediastinal masses, and in staging of SCLC
Where is incision made for mediastinoscopy?
2-3cm incision in midline of lower neck in the suprasternal notch
This artery is immediately anterior to the mediastinoscope
The innominate artery (brachiocephalic artery)
Anesthetic considerations for mediastinoscopy
GETA
A-line and pulse ox on the right side to monitor for compression of the innominate artery (if waveform flattens, as the surgeon to reposition the scope)
NIBP on left
Trachea may be compressed by the scope
Keep patient paralyzed! Coughing could be devastating. in terms of resultant blood loss.
T&C should be complete with blood available IN the room!
Why is compression of the innominate artery bad?
It also supplies the right carotid! Can result in poor cerebral perfusion
Major things to watch for during mediastinoscopy
Compression of the innominate artery
Compression of the trachea
Risk for hemorrhage (8% overall mortality)
This is an absolute contraindication for mediastinoscopy
A prior mediastinoscopy! Major risk for mortality d/t formation of adhesions.
Major complications of mediastinoscopy
Hemorrhage Pneumothorax RLN injury Phrenic nerve injury Esophageal injury Air embolism Left hemiparesis (from compression of innominate)
VATS is the procedure of choice for
Diagnosis and management of diseases of the pleura, non diagnosed peripheral pulmonary nodules, interstitial lung disease, lung biopsies, pleurectomies, and other various pulmonary disorders
Can VATS be done supine?
Yes, but generally done lateral
Advantages of VATS compared to open thoracotomy
Less pain
Shorter hospital stay
Improved post-op PFTs (probe due to decreased pain)
Injury risk in the lateral position
Risk for stretch and compression injury! Stretch injury in up arm and compression in down arm.
Make sure to watch eyes and ears.
Risk for damage to the perennial nerve –> dependent leg should be slightly flexed.
Empyema can lead to
Erosion of the bronchus and development of a bronchopleural fistula
S/S of bronchopleural fistula
SQ emphysema, dyspnea, tracheal deviation, air leak (bubbbles in chest tube), and purulent chest tube drainage
Indication for tracheal resection
For tracheal obstruction. ETT should be placed past the obstruction if possible (use fiberoptic). If not, then ventilate with HFJV.
Post-op notes for tracheal resection.
Transport with HOB up and neck flexed to prevent tension at the suture line.
Caution with the ETT cuff –> make sure that the cuff didn’t get sutured in place during closure of the trachea.
